U.S. patent number 9,503,942 [Application Number 14/136,074] was granted by the patent office on 2016-11-22 for selection of air interface protocol based on spectral efficiency.
This patent grant is currently assigned to Sprint Spectrum L.P.. The grantee listed for this patent is Sprint Spectrum L.P.. Invention is credited to Sreekar Marupaduga, John W. Prock, Young Zhao.
United States Patent |
9,503,942 |
Prock , et al. |
November 22, 2016 |
Selection of air interface protocol based on spectral
efficiency
Abstract
A method and system is disclosed for selection of an air
interface protocol based on spectral efficiency (SE). When a
request for service is received from a wireless communication
device on a first air interface, a requested SE of the request will
be determined, and a first ratio of the requested SE to an average
SE on the first air interface computed. If the first ratio is
greater than a threshold, the requested service will be provided on
the first air interface. Otherwise, a projected SE of providing the
requested service on a second air interface will be determined, and
a second ratio of the projected SE to an average SE on the second
air interface computed. If the first ratio is greater than the
second ratio, the requested service will be provided on the first
air interface. Otherwise, the requested service will be provided on
the second air interface.
Inventors: |
Prock; John W. (Raymore,
MO), Zhao; Young (Overland Park, KS), Marupaduga;
Sreekar (Overland Park, KS) |
Applicant: |
Name |
City |
State |
Country |
Type |
Sprint Spectrum L.P. |
Overland Park |
KS |
US |
|
|
Assignee: |
Sprint Spectrum L.P. (Overland
Park, KS)
|
Family
ID: |
57287826 |
Appl.
No.: |
14/136,074 |
Filed: |
December 20, 2013 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W
48/18 (20130101) |
Current International
Class: |
H04W
4/00 (20090101); H04W 36/00 (20090101) |
Field of
Search: |
;370/331 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cheng; Peter
Claims
We claim:
1. In a wireless communication system comprising a first radio
access network (RAN) configured to serve wireless communication
devices (WCDs) on a first air interface according to a first air
interface protocol, a second RAN configured to serve WCDs on a
second air interface according to a second air interface protocol,
and a network device communicatively connected to both the first
and second RANs, a method comprising: at the first RAN, receiving a
wireless transmission on the first air interface from a WCD
including a message requesting a wireless service from the first
RAN, the message including information indicative of a requested
spectral efficiency for the requested wireless service, wherein the
spectral efficiency corresponds to a metric of bit rate per
utilized bandwidth; at the network device, receiving the
information indicative of the requested spectral efficiency; based
on the information, determining by the network device the requested
spectral efficiency for providing the requested wireless service on
the first air interface of the first RAN according to the first air
interface protocol; at the network device, making a comparison of
the requested spectral efficiency with at least one of (a) a
threshold, or (b) a projected spectral efficiency for providing the
requested wireless service on the second air interface of the
second RAN according to the second air interface protocol; and
based on the comparison, providing the WCD the requested wireless
service on one of (i) the first air interface of the first RAN
according to the first air interface protocol, or (ii) the second
air interface of the second RAN according to the second air
interface protocol; wherein the requested wireless service
comprises a wireless communication service.
2. The method of claim 1, wherein receiving information comprises
receiving the information from the first RAN upon the first RAN
receiving the message from the WCD requesting the wireless
service.
3. The method of claim 2, wherein the first RAN includes a base
station having an air interface configured to operate according to
the first air interface protocol, wherein the network device is at
least one of co-located with the first RAN or co-located with the
base station, and wherein the first RAN receiving the message from
the WCD requesting the wireless service comprises the base station
receiving the the message from the WCD on the air interface.
4. The method of claim 1, wherein the information includes a
channel quality indicator (CQI) index, and wherein determining the
requested spectral efficiency for providing the requested wireless
service on the first air interface of the first RAN comprises
looking up a spectral efficiency in a CQI table based on the CQI
index.
5. The method of claim 1, wherein, based on the comparison,
providing the WCD the requested wireless service on one of (i) the
first air interface of the first RAN according to the first air
interface protocol, or (ii) the second air interface of the second
RAN according to the second air interface protocol comprises:
determining a first ratio of the requested spectral efficiency to a
first average spectral efficiency measured on the first air
interface of the first RAN; if the determined first ratio is
greater than or equal to the threshold, then providing the WCD the
requested wireless service on the first air interface of the first
RAN according to the first air interface protocol; if the
determined first ratio is less than the threshold, then determining
a second ratio of the projected spectral efficiency to a second
average spectral efficiency measured on the second air interface of
the second RAN; if the determined first ratio is less than the
threshold and the determined first ratio is also greater than or
equal to the determined second ratio, then providing the WCD the
requested wireless service on the first air interface of the first
RAN according to the first air interface protocol; and if the
determined first ratio is less than the threshold and the
determined first ratio is also less than the determined second
ratio, then providing the WCD the requested wireless service on the
second air interface of the second RAN according to the second air
interface protocol.
6. The method of claim 5, wherein determining the first ratio
comprises determining the first average spectral efficiency as a
running time average of spectral efficiencies of communications
carried on the first air interface between the first RAN and one or
more WCDs served by the first RAN.
7. The method of claim 5, wherein determining the second ratio
comprises: determining the projected spectral efficiency for
providing the requested wireless service on the second air
interface of the second RAN; and determining the second average
spectral efficiency as a running time average of spectral
efficiencies of communications carried on the second air interface
between the second RAN and one or more WCDs served by the second
RAN.
8. The method of claim 7, wherein determining the projected
spectral efficiency for providing the requested wireless service on
the second air interface of the second RAN comprises: determining a
projected data rate supported on the second air interface of the
second RAN between the second RAN and the WCD; and dividing the
determined projected data rate by a bandwidth used for carrying
communications on the second air interface of the second RAN
between the second RAN and WCDs served by the second RAN.
9. The method of claim 1, wherein the first air interface protocol
is Long Term Evolution (LTE), and the first air interface operates
according to LTE specifications, and wherein the second air
interface protocol is selected from the group consisting of
Evolution-Data Optimized (EVDO) and Universal Mobile
Telecommunications System (UMTS), and the second air interface
operates according to one of EVDO specifications or UMTS
specification.
10. The method of claim 1, wherein the first RAN and the second RAN
are configured within the wireless communication system as one of
co-located or neighboring.
11. A network device comprising: at least one network communication
interface communicatively coupled to both a first radio access
network (RAN) and a second RAN, wherein the first RAN is configured
to serve wireless communication devices (WCDs) on a first air
interface according to a first air interface protocol, and the
second RAN is configured to serve WCDs on a second air interface
according to a second air interface protocol; and one or more
processors for executing instructions that cause the network device
to carry out functions including: receiving information indicative
of a requested spectral efficiency for a wireless service requested
of the first RAN by a WCD, wherein the information is received by
the network device from the first RAN upon receipt by the first RAN
on the first air interface of a message from the WCD requesting the
wireless service, the information being included in the message,
and wherein the spectral efficiency corresponds to a metric of bit
rate per utilized bandwidth, based on the information, determining
the requested spectral efficiency for providing the requested
wireless service on the first air interface of the first RAN
according to the first air interface protocol, making a comparison
of the requested spectral efficiency with at least one of (a) a
threshold, or (b) a projected spectral efficiency for providing the
requested wireless service on the second air interface of the
second RAN according to the second air interface protocol, and
based on the comparison, providing the WCD the requested wireless
service on one of (i) the first air interface of the first RAN
according to the first air interface protocol, or (ii) the second
air interface of the second RAN according to the second air
interface protocol; wherein the requested wireless service
comprises a wireless communication service.
12. The network device of claim 11, wherein the information
includes a channel quality indicator (CQI) index, and wherein
determining the requested spectral efficiency for providing the
requested wireless service on the first air interface of the first
RAN comprises looking up a spectral efficiency in a CQI table based
on the CQI index.
13. The network device of claim 11, wherein, based on the
comparison, providing the WCD the requested wireless service on one
of (i) the first air interface of the first RAN according to the
first air interface protocol, or (ii) the second air interface of
the second RAN according to the second air interface protocol
comprises: determining a first ratio of the requested spectral
efficiency to a first average spectral efficiency measured on the
first air interface of the first RAN; if the determined first ratio
is greater than or equal to the threshold, then providing the WCD
the requested wireless service on the first air interface of the
first RAN according to the first air interface protocol; if the
determined first ratio is less than the threshold, then determining
a second ratio of the projected spectral efficiency to a second
average spectral efficiency measured on the second air interface of
the second RAN; if the determined first ratio is less than the
threshold and the determined first ratio is also greater than or
equal to the determined second ratio, then providing the WCD the
requested wireless service on the first air interface of the first
RAN according to the first air interface protocol; and if the
determined first ratio is less than the threshold and the
determined first ratio is also less than the determined second
ratio, then providing the WCD the requested wireless service on the
second air interface of the second RAN according to the second air
interface protocol.
14. The network device of claim 13, wherein determining the first
ratio comprises determining the first average spectral efficiency
as a running time average of spectral efficiencies of
communications carried on the first air interface between the first
RAN and one or more WCDs served by the first RAN.
15. The network device of claim 13, wherein determining the second
ratio comprises: determining the projected spectral efficiency for
providing the requested wireless service on the second air
interface of the second RAN; and determining the second average
spectral efficiency as a running time average of spectral
efficiencies of communications carried on the second air interface
between the second RAN and one or more WCDs served by the second
RAN.
16. The network device of claim 15, wherein determining the
projected spectral efficiency for providing the requested wireless
service on the second air interface of the second RAN comprises:
determining a projected data rate supported on the second air
interface of the second RAN between the second RAN and the WCD; and
dividing the determined projected data rate by a bandwidth used for
carrying communications on the second air interface of the second
RAN between the second RAN and WCDs served by the second RAN.
17. The network device of claim 11, wherein the first air interface
protocol is Long Term Evolution (LTE), and the first air interface
operates according to LTE specifications, and wherein the second
air interface protocol is selected from the group consisting of
Evolution-Data Optimized (EVDO) and Universal Mobile
Telecommunications System (UMTS), and the second air interface
operates according to one of EVDO specifications or UMTS
specification.
18. The network device of claim 11, wherein the first RAN and the
second RAN are configured within a wireless communication system as
one of co-located or neighboring, wherein the first RAN includes a
base station having an air interface configured to operate
according to the first air interface protocol, wherein the network
device is at least one of co-located with the first RAN or
co-located with the base station.
19. A non-transitory computer-readable medium having instructions
stored thereon that, upon execution by one or more processors of a
network device communicatively coupled to both a first radio access
network (RAN) configured to serve wireless communication devices
(WCDs) on a first air interface according to a first air interface
protocol, and a second RAN configured to serve WCDs on a second air
interface according to a second air interface protocol, cause the
network device to carry out functions including: receiving
information indicative of a requested spectral efficiency for a
wireless service requested of the first RAN by a WCD, wherein the
information is received by the network device from the first RAN
upon receipt by the first RAN on the first air interface of a
message from the WCD requesting the wireless service, the
information being included in the message, and wherein the spectral
efficiency corresponds to a metric of bit rate per utilized
bandwidth; based on the information, determining the requested
spectral efficiency for providing the requested wireless service on
the first air interface of the first RAN according to the first air
interface protocol; making a comparison of the requested spectral
efficiency with at least one of (a) a threshold, or (b) a projected
spectral efficiency for providing the requested wireless service on
the second air interface of the second RAN according to the second
air interface protocol, and based on the comparison, providing the
WCD the requested wireless service on one of (i) the first air
interface of the first RAN according to the first air interface
protocol, or (ii) the second air interface of the second RAN
according to the second air interface protocol; wherein the
requested wireless service comprises a wireless communication
service.
20. The non-transitory computer-readable medium of claim 19,
wherein, based on the comparison, providing the WCD the requested
wireless service on one of (i) the first air interface of the first
RAN according to the first air interface protocol, or (ii) the
second air interface of the second RAN according to the second air
interface protocol comprises: determining a first ratio of the
requested spectral efficiency to a first average spectral
efficiency measured on the first air interface of the first RAN; if
the determined first ratio is greater than or equal to the
threshold, then providing the WCD the requested wireless service on
the first air interface of the first RAN according to the first air
interface protocol; if the determined first ratio is less than the
threshold, then determining a second ratio of the projected
spectral efficiency to a second average spectral efficiency
measured on the second air interface of the second RAN; if the
determined first ratio is less than the threshold and the
determined first ratio is also greater than or equal to the
determined second ratio, then providing the WCD the requested
wireless service on the first air interface of the first RAN
according to the first air interface protocol; and if the
determined first ratio is less than the threshold and the
determined first ratio is also less than the determined second
ratio, then providing the WCD the requested wireless service on the
second air interface of the second RAN according to the second air
interface protocol.
Description
BACKGROUND
In a typical cellular radio communication system (wireless
communication system), an area is divided geographically into a
number of cell sites, each defined by a radio frequency (RF)
radiation pattern from a respective antenna or antenna system. The
antennas in the cells are in turn coupled to one or another form of
controller, which is then coupled to a telecommunications switch or
gateway, such as a mobile switching center (MSC) and/or a packet
data serving node (PDSN) for instance. These (and possibly other)
elements function collectively to form a Radio Access Network (RAN)
of the wireless communication system. The switch or gateway may
then be coupled with a transport network, such as the PSTN or a
packet-switched network (e.g., the Internet).
Depending on the specific underlying technologies and architecture
of a given wireless communication system, the RAN elements may take
different forms. In a code division multiple access (CDMA) system
configured to operate according IS-2000 and IS-856 standards, for
example, the antenna system is referred to as a base transceiver
system (BTS), and is usually under the control of a base station
controller (BSC). In a universal mobile telecommunications system
(UMTS) configured to operate according to ITU IMT-2000 standards,
the antenna system is usually referred to as a NodeB, and is
usually under the control of a radio network controller (RNC).
Other architectures and operational configurations of a RAN are
possible as well.
A subscriber (or user) in a service provider's wireless
communication system accesses the system for communication services
via a Wireless Communication Device ("WCD"), such as a cellular
telephone, "smart" phone, pager, or appropriately equipped portable
computer, for instance. In a CDMA system a WCD is referred to as an
access terminal ("AT"); in a UMTS system a WCD is referred to as
User Equipment ("UE"). For purposes of the discussion herein, the
term WCD will be used to refer to either an AT or UE or the like.
When a WCD is positioned in a cell, it communicates via an RF air
interface with the BTS or NodeB antenna of the cell. Consequently,
a communication path or "channel" is established between the WCD
and the transport network, via the air interface, the BTS or NodeB,
the BSC or RNC, and the switch or gateway.
As the demand for wireless communications has grown, the volume of
call traffic in most cell sites has correspondingly increased. To
help manage the call traffic, most cells in a wireless network are
usually further divided geographically into a number of sectors,
each defined respectively by radiation patterns from directional
antenna components of the respective BTS or NodeB, or by respective
antennas. These sectors can be referred to as "physical sectors,"
since they are physical areas of a cell site. Therefore, at any
given instant, a WCD in a wireless network will typically be
positioned in a given physical sector and will be able to
communicate with the transport network via the BTS or NodeB serving
that physical sector.
The functional combination of a BTS of a cell or sector with a BSC,
or of a NodeB and an RNC, is commonly referred to as a "base
station." The actual physical of a configuration of a base station
can range from an integrated BTS-BSC or NodeB-RNC unit to a
distributed deployment of multiple BTSs under a single BSC, or
multiple NodeBs under a single RNC. A base station may be typically
deployed to provide coverage over a geographical area on a scale of
a few to several square miles and for tens to hundreds to several
thousands (or more) of subscribers at any one time.
As a subscriber at a WCD moves between wireless coverage areas of a
wireless communication system, such as between cells or sectors, or
when network conditions change or for other reasons, the WCD may
"hand off" from operating in one coverage area to operating in
another coverage area. In a usual case, this handoff process is
triggered by the WCD monitoring the signal strength of various
nearby available coverage areas, and the BSC or RNC (or other
controlling network entity) determining when one or more threshold
criteria are met. For instance, a WCD may continuously monitor
signal strength from various available sectors and notify a BSC
when a given sector has a signal strength that is sufficiently
higher than the sector in which the WCD is currently operating. The
BSC may then direct the WCD to hand off to that other sector. By
convention, a WCD is said to handoff from a "source" cell or sector
(or base station) to a "target" cell or sector (or base
station).
In some wireless communication systems or markets, a wireless
service provider may implement more than one type of air interface
protocol. For example, a carrier may support one or another version
of CDMA, such as EIA/TIA/IS-2000 Rel. 0, A, and CDMA 2000 Spread
Spectrum Systems Revision E (collectively referred to generally
herein as "IS-2000") for both circuit-cellular voice and data
traffic, as well as a more exclusively packet-data-oriented
protocol such as EIA/TIA/IS-856 Rel. 0, A, or other version thereof
(hereafter "IS-856"). Under IS-2000, packet-data communications may
be referred to as 1X Radio Transmission Technology ("1X-RTT")
communications, also abbreviated as just "1X." However, since
IS-2000 supports both circuit voice and packet data communications,
the term 1X (or 1X-RTT) is sometimes used to more generally refer
the IS-2000 air interface, without regard to the particular type of
communication carried. Packet-data communications under IS-856 are
conventionally referred to as Evolution-Data Optimized ("EVDO")
communications, also abbreviated as just "DO." A carrier could also
implement an orthogonal frequency division multiple access (OFDMA)
based system according to protocols specified by third generation
partnership project (3GPP) Long Term Evolution ("LTE") Advanced,
for example. WCDs may be capable of communication under any or all
such protocols, and may further be capable of handing off between
them, in addition to being able to hand off between various
configurations of coverage areas.
OVERVIEW
As noted above, a WCD may be capable of operating under more than
one air-interface protocol. More particularly, a WCD may include
one or more transceiver components that, coupled with one or more
antennas, provide a multi-technology air interface capable of
transmitting and receiving wireless signals according to each of
multiple, different physical radio transmission/reception
technologies. A multi-technology air interface can be viewed as
including multiple air interfaces, each based on a respective
air-interface technology, and each configured to operate according
to a respective air-interface protocol. Such a WCD may thus be
capable of operating under various, different air interface
protocols, and/or according to various, different air-interface
technologies. For operation in the context of a RAN, an
air-interface technology may also be considered a radio access
technology. Expanding on the list of examples given above,
different air-interface technologies and protocols could include
1.times.RTT, 1.times.EV-DO, LTE, WiMAX, iDEN, TDMA, AMPS, GSM,
GPRS, UMTS, EDGE, MMDS, WI-FI, and BLUETOOTH, for example.
Also as noted above, a service provider may operate RANs that
support multiple air interface technologies. For example, a service
provider's wireless communication system could include CDMA RANs
for voice calls, and both EVDO RANs and LTE RANs for data. Further,
air interface components of different RANs could be deployed to
provide neighboring coverage, overlapping coverage, and/or
co-located coverage for CDMA, EVDO, and LTE (or other air interface
technologies). For example, CDMA and EVDO air interfaces are
sometimes configured in co-located hybrid BTS/BSC systems of what
is referred to herein as a "CDMA/EVDO" RAN. LTE air interfaces
could be configured in neighboring or co-located LTE RANs such that
LTE and CDMA/EVDO services overlap within at least some regions of
the wireless communication system.
In such wireless communication system, a multi-technology WCD might
place and receive voice calls on the CDMA air interface, and might
obtain data services on the LTE air interface or the EVDO air
interface. For data services in particular, it may happen that LTE
is a default or preferred type of service when both LTE and EVDO
air interfaces are available for providing service to a WCD. This
could be the case, for example, because LTE typically (but not
always) supports generally higher data transmission rates (e.g.,
bits per second). However, it can also be the case that for a given
data rate, the spectral efficiency (i.e., bits per second per
bandwidth used) of LTE service compared to that of EVDO service is
such that EVDO service might be a better and/or advantageous
choice. It would therefore be desirable to be able to consider
relative spectral efficiencies of LTE and EVDO service when
selecting which to provide to a WCD. Accordingly, example
embodiments herein provide for selection of an air interface for
service based on spectral efficiency.
Hence, in one respect, various embodiments of the present invention
provide, in a communication system comprising a first radio access
network (RAN) configured to serve wireless communication devices
(WCDs) on a first air interface according to a first air interface
protocol, a second RAN configured to serve WCDs on a second air
interface according to a second air interface protocol, and a
network device communicatively connected to both the first and
second RANs, a method comprising: at the network device, receiving
information indicative of a requested spectral efficiency for a
service to be provided by the first RAN to a WCD, the first RAN
having received a request for the service from the WCD on the first
air interface, and the information having been included in the
request for the service; based on the information, determining by
the network device the requested spectral efficiency for providing
the requested service on the first air interface of the first RAN
according to the first air interface protocol; and the network
device making a determination to provide the WCD the requested
service on one of (i) the first air interface of the first RAN
according to the first air interface protocol, or (ii) the second
air interface of the second RAN according to the second air
interface protocol, the determination being based on a comparison
of the requested spectral efficiency to at least one of (a) a
threshold, or (b) a projected spectral efficiency for providing the
requested service on the second air interface of the second RAN
according to the second air interface protocol.
In another respect, various embodiments of the present invention
provide a network device comprising: at least one network
communication interface communicatively coupled to both a first
radio access network (RAN) and a second RAN, wherein the first RAN
is configured to serve wireless communication devices (WCDs) on a
first air interface according to a first air interface protocol,
and the second RAN is configured to serve WCDs on a second air
interface according to a second air interface protocol; one or more
processors; memory accessible by the one or more processors; and
machine-readable instructions stored in the memory, that upon
execution by the one or more processors cause the network device to
carry out functions including: receiving information indicative of
a requested spectral efficiency for a service to be provided by the
first RAN to a WCD, wherein the information is received from the
first RAN upon receipt by the first RAN of a request for the
service from the WCD on the first air interface, and the
information is included in the request for the service, based on
the information, determining the requested spectral efficiency for
providing the requested service on the first air interface of the
first RAN according to the first air interface protocol, and making
a determination to provide the WCD the requested service on one of
(i) the first air interface of the first RAN according to the first
air interface protocol, or (ii) the second air interface of the
second RAN according to the second air interface protocol, wherein
the determination is based on a comparison of the requested
spectral efficiency to at least one of (a) a threshold, or (b) a
projected spectral efficiency for providing the requested service
on the second air interface of the second RAN according to the
second air interface protocol.
In still another respect, various embodiments of the present
invention provide a non-transitory computer-readable medium having
instructions stored thereon that, upon execution by one or more
processors of a network device communicatively coupled to both a
first radio access network (RAN) configured to serve wireless
communication devices (WCDs) on a first air interface according to
a first air interface protocol, and a second RAN configured to
serve WCDs on a second air interface according to a second air
interface protocol, cause the network device to carry out functions
including: receiving information indicative of a requested spectral
efficiency for a service to be provided by the first RAN to a WCD,
wherein the information is received from the first RAN upon receipt
by the first RAN of a request for the service from the WCD on the
first air interface, and the information is included in the request
for the service; based on the information, determining the
requested spectral efficiency for providing the requested service
on the first air interface of the first RAN according to the first
air interface protocol; and making a determination to provide the
WCD the requested service on one of (i) the first air interface of
the first RAN according to the first air interface protocol, or
(ii) the second air interface of the second RAN according to the
second air interface protocol, wherein the determination is based
on a comparison of the requested spectral efficiency to at least
one of (a) a threshold, or (b) a projected spectral efficiency for
providing the requested service on the second air interface of the
second RAN according to the second air interface protocol.
These as well as other aspects, advantages, and alternatives will
become apparent to those of ordinary skill in the art by reading
the following detailed description, with reference where
appropriate to the accompanying drawings. Further, it should be
understood that this summary and other descriptions and figures
provided herein are intended to illustrate the invention by way of
example only and, as such, that numerous variations are possible.
For instance, structural elements and process steps can be
rearranged, combined, distributed, eliminated, or otherwise
changed, while remaining within the scope of the invention as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart depicting an example embodiment of a method
selection of an air interface protocol based on spectral
efficiency, in accordance with example embodiments.
FIG. 2 is a simplified block diagram of two example RANs of an
example of wireless communication system in which selection of an
air interface protocol based on spectral efficiency could be
implemented, in accordance with example embodiments.
FIG. 3 is a simplified block diagram of an example multi-modal RAN
of an example of wireless communication system in which selection
of an air interface protocol based on spectral efficiency could be
implemented, in accordance with example embodiments.
FIG. 4 is an example table of channel quality index that could be
used in selecting an air interface protocol based on spectral
efficiency, in accordance with example embodiments.
FIG. 5 is an example table of data rate parameters that could be
used selecting an air interface protocol based on spectral
efficiency, in accordance with example embodiments.
FIG. 6 is a flowchart depicting an example program logic of an
example of method selection of an air interface protocol based on
spectral efficiency, in accordance with example embodiments.
FIG. 7 is a simplified block diagram of an example network device
configured for carrying out selection of an air interface protocol
based on spectral efficiency, in accordance with example
embodiments.
DETAILED DESCRIPTION
Example embodiments presented herein will be described by way of
example with reference to wireless communication systems. It will
be appreciated that wireless communication systems can employ a
range of technologies designed to operate according to a number of
related standards and protocols, including, without limitation, LTE
Advanced, IS-2000, IS-856 (EVDO), IMT-2000, WiMax, and WiFi, among
others, in order to deliver both circuit-cellular and wireless
packet-data services. Underlying access technologies include CDMA,
time division multiple access (TDMA), and orthogonal frequency
division multiple access (OFDMA), among others.
Wireless communications systems can generally be classified under
the umbrella of one or another representative system architecture.
One example is a "CDMA network," which, despite its label, can
include both CDMA-based wireless access (e.g., as specified under
IS-2000) and TDMA-based wireless access (e.g., as specified under
IS-856), among other technologies. The terms "EVDO" and "CDMA/EVDO"
will be used interchangeably herein in reference to data services
in a CDMA network, unless specified otherwise. Other examples of
representative architectures include "UMTS networks," which also
can include CDMA-based wireless access (e.g., as specified under
IMT-2000), and "LTE Advanced networks," which can include
OFDMA-based wireless access, and are sometimes considered as
next-generation variants of, and deployed within, UMTS networks.
For purposes of the discussion herein, the terms "LTE" and "LTE
Advanced" will be used interchangeably, unless specified
otherwise.
FIG. 1 is a flowchart depicting an example embodiment of a method
of selection of an air interface protocol based on spectral
efficiency, carried out by a network device communicatively
connected to both a first RAN and a second RAN of a wireless
communication system. In accordance with example embodiments, the
first RAN could be configured to serve WCDs on a first air
interface according to a first air interface protocol, and the
second RAN could be configured to serve WCDs on a second air
interface according to a second air interface protocol. By way of
example, the first RAN could be configured to operate according to
LTE, with one or more LTE air interfaces, and could include one or
more eNodeBs or other LTE base station devices. Also by way of
example, the second RAN could be configured to operate according to
EVDO or UMTS, with one or more EVDO or UMTS air interfaces, and
could include one or more BTSs, eNodeBs, mobility management
entities (MMEs), BSC, and/or RNCs.
The steps of the flowchart in FIG. 1 could be implemented as
machine-language instructions stored in a non-transient computer
readable medium of the network device, and executable by one or
more processors of the network device in order to cause the network
device to carry out the functions and operations described by way
of example below. Non-limiting examples of the network device could
include a BSC, eNodeB, MME, or other RAN component or network node
configured to operate in a wireless communication system.
At step 102, the network device receives information indicative of
a requested spectral efficiency for a service to be provided by the
first RAN to a WCD. More particularly, the first RAN could receive
a request for the service from the WCD on the first air interface,
and the request could include the information indicating the
requested spectral efficiency for the requested service. Upon
receiving the service request, the first RAN could then send the
information to the network device.
At step 104, the network device could use the received information
to determine the requested spectral efficiency for providing the
requested service on the first air interface of the first RAN
according to the first air interface protocol. By way of example,
if the first air interface protocol is taken to be LTE, then the
information could be a channel quality indicator (CQI) index
included by the WCD in its service request to the first RAN. The
network device could then determine the requested spectral
efficiency by looking up the CQI index in a CQI table in its
non-transient computer readable medium (or other form of memory),
and determining a tabulated spectral efficiency associated with the
CQI index. Other forms of information indicative of requested
spectral efficiency could be used as well, as could other
techniques for determining the requested spectral efficiency from
the information.
Finally, at step 106, the network device could make a determination
to provide the WCD the requested service either on (i) the first
air interface of the first RAN according to the first air interface
protocol, or on (ii) the second air interface of the second RAN
according to the second air interface protocol. In accordance with
example embodiments, the determination could be made by comparing
the requested spectral efficiency to either (a) a threshold, or (b)
a projected spectral efficiency for providing the requested service
on the second air interface of the second RAN according to the
second air interface protocol. Furthermore, the comparison could
involve both the threshold and the projected spectral efficiency,
as described below.
In accordance with example embodiments, making the determination of
which of the first or second RANs should provide the requested
service could entail evaluating the requested and projected
spectral efficiencies for providing the requested service, in view
of average spectral efficiencies measured on the respective first
and second air interfaces. More particularly, the network device
could determine a first ratio of the requested spectral efficiency
to a first average spectral efficiency measured on the first air
interface of the first RAN. The network device could then compare
the determined first ratio to a threshold value. If the determined
first ratio is found to be greater than or equal to the threshold,
then the network device could select the first air interface for
providing the requested service to the WCD, and the first RAN could
provide the requested service according to the first air interface
protocol.
If instead the determined first ratio is found to be less than the
threshold, then the network device could make a further
determination involving the projected spectral efficiency.
Specifically, in this case, the network device could determine a
second ratio of the projected spectral efficiency to a second
average spectral efficiency measured on the second air interface of
the second RAN. The network device could then compare the
determined first ratio to the determined second ratio. If the
determined first ratio is found to be greater than or equal to the
determined second ratio, in addition to having already been found
to be less than the threshold, then the network device could again
select the first air interface for providing the requested service
to the WCD, and the first RAN could provide the requested service
according to the first air interface protocol.
If instead, the determined first ratio is found to be less than the
determined second ratio, in addition to having already been found
to be less than the threshold, then the network device could select
the second air interface for providing the requested service to the
WCD. In this case, the second RAN could provide the requested
service according to the second air interface protocol.
In accordance with example embodiments, the first average spectral
efficiency could correspond to a running time average of spectral
efficiencies of communications carried on the first air interface
between the first RAN and one or more other WCDs served by the
first RAN. Again assuming, by way of example, that the first air
interface protocol is LTE, then the network device could maintain a
record of CQI indexes of communication services provided by the
first RAN over a time window reaching backward from the time at
which the WCD request of step 102 was received. Each of the CQI
indexes in the window could be translated to an associated spectral
efficiency and all associated spectral efficiencies could be
averaged to determine the first average spectral efficiency. It
will be appreciated that other forms of time averaged spectral
efficiency could be devised. For example, a time weighting (e.g.,
respective duration of each communication service) could be applied
to each of the spectral efficiencies during the time window, the
weighted spectral efficiencies summed, and the sum divided by the
duration of the time window (or divided by the sum of the weighting
factors). Furthermore, the time window could be defined in
different ways with respect to duration, and the times at its
boundaries (beginning and ending points). Further still, the
network device could query the first RAN for the average spectral
efficiency.
Also in accordance with example embodiments, the network device
could determine the second ratio of the projected spectral
efficiency to the second average spectral efficiency by first
determining the projected spectral efficiency for providing the
requested service on the second air interface of the second RAN.
More specifically, the network device could first query the WCD for
an indication of a projected data rate that can be supported on the
second air interface from the second RAN. For example, if the
second RAN has an EVDO air interface and operates according EVDO,
the network device could send request to the WCD via the first RAN
for a "data rate control" (DRC) value. As explained below, a WCD
monitors a signal-to-noise ratio on a forward link from its serving
base station to determine a supported data rate. The supported data
rate is encoded in a DRC request, and transmitted to the serving
base station. Thus, by querying the WCD for a DRC value and
decoding the DRC value so obtained, the network device could derive
a projected data rate (e.g., bits per second) for providing the
requested service on the EVDO interface. The network device could
then determine the projected (EVDO) spectral efficiency by dividing
the projected data rate by the EVDO channel bandwidth (e.g., 1.25
MHz, as described below).
Similarly to the first average spectral efficiency, the second
average spectral efficiency could correspond to a running time
average of spectral efficiencies of communications carried on the
second air interface between the second RAN and one or more other
WCDs served by the second RAN. Again for the example of an EVDO
RAN, the network device could determine the data rates of
communication services provided by the second (EVDO) RAN over a
time window reaching backward from the time at which the WCD
request of step 102 was received. More specifically, the network
device could query the EVDO RAN for a history of DRC values
received from WCDs during the time window. Dividing the data rates
corresponding to the historical DRC values by the EVDO channel
bandwidth would then give corresponding spectral efficiencies used
during the time window. These could be averaged in a manner similar
to that described for the first average spectral efficiency, and
the second ratio then computed from the projected spectral
efficiency and the second average spectral efficiency. Again, the
network device could query the second RAN for the projected
spectral efficiency, the average spectral efficiency, or both.
In accordance with example embodiments, the first and second RANs
could be co-located, or possibly neighboring. Herein, neighboring
RANs are taken to be RANs in close enough proximity to be capable
or suitable for serving the same WCD at a given location. An
example of such a configuration is first and second RANs with one
or more overlapping coverage areas (e.g., cells or sectors).
Also in accordance with example embodiments, the network device
could be co-located with one or another or both of the first and
second RAN. Example configurations illustrating these different
possible relative locations of the network device and the first and
second RANs are described below.
It will be appreciated that the example embodiment illustrated in
FIG. 1 could include alternate and/or additional steps, while still
remaining within the scope and spirit of example embodiments
herein. Furthermore, unless stated otherwise, conditional
operations that can be expressed in a mathematical form such as "if
x y, then do a; if x<y, then do b" or the like, can generally be
exchanged with alternate forms expressed as "if x>y, then do a;
if x<y, then do b," while still achieving the same intended
operational principles of the example embodiments.
FIG. 2 shows a simplified block diagram of an example wireless
network 200 that can be operated by a wireless service provider,
and in which an example method of selection of an air interface
protocol based on spectral efficiency. By way of example, the
network 200 includes RAN 204 configured to support both CDMA-based
air interface communications (e.g., as specified under both IS-2000
and IS-856), RAN 205 configured to support OFDMA-based air
interface communications (e.g., as specified under LTE Advanced).
For convenience in discussing the example embodiments presented
herein, the term "EVDO RAN" will be used for referring to the RAN
204, and the term "LTE RAN" will be used for referring to the RAN
205. It will be appreciated that a network such as network 300
could include support for other types of air-interface technologies
as well.
The EVDO RAN 204 includes a CDMA BTS 206 with a CDMA/EVDO air
interface antenna 206-T for providing services according to
CDMA/EVDO. The LTE RAN 205 includes an LTE eNodeB 200 with an LTE
air interface antenna 208-T for providing services according to
LTE.
The example illustrated in FIG. 2 also shows three WCDs 202-1,
202-2, and 202-3, each depicted as having at least one active air
interface of a particular type with one or another of the antennas
206-T or 208-T. Specifically, the WCD 202-1 has an air interface
201-1 with the LTE RAN 205 via the eNodeB 208 and the associated
antenna 208-T. The WCD 202-2 has an air interface 203-1 also with
the EVDO RAN 204 via the BTS 206 and the associated antenna 206-T.
The WCD 202-2 has two different air interfaces: an air interface
203-2 with the EVDO RAN 204 via the BTS 206 and the associated
antenna 206-T, and an air interface 207-2 with the LTE RAN 205 via
the eNodeB 208 and the associated antenna 208-T.
As a visual cue, the LTE air interfaces are depicted as
white-filled "lightning bolts," and the EVDO air interfaces are
depicted as blackened "lightning bolts." The two air interfaces
207-2 and 203-2 depicted for the WCD 202-3 may be taken as
representing a capability of the WCD 202-3 to operate according to
either air interface separately, and/or to operate according to
both concurrently.
For communications under LTE (or LTE Advanced) based protocols,
subscribers may engage in communications via the eNodeB 208 and the
associated antenna 208-T from the WCD 202-1 over air interface
207-1 and/or from the WCD 202-3 over air interface 207-2.
Transmissions over the air interface 207-1 from the antenna 208-T
to the WCD 202-1 represent a "downlink" from the eNodeB 208 to the
WCD 202-1, while transmissions over air interface 207-1 from the
WCD 202-1 to the antenna 208-T represent an "uplink" from the WCD
202-1. Similarly, transmissions over the air interface 207-2 from
the antenna 208-T to the WCD 202-3 represent a downlink from the
eNodeB 208 to the WCD 202-3, while transmissions over air interface
207-2 from the WCD 202-3 to the antenna 208-T represent an uplink
from the WCD 202-3. Under LTE Advanced, the downlink operates
according to OFDMA, while the uplink operates according to Single
Carrier Frequency Division Multiple Access (SC-FDMA).
The eNodeB 208 may be connected to a serving gateway S-GW 216,
which in turn may be connected to an internet 222 via a packet data
network gateway PDN-GW 218. The eNodeB 208 could also be connected
to the S-GW 216 by way of a mobility management entity MME 214,
which may also be configured to control communications between the
eNodeB 208 and one or more other eNodeBs in the network. The MME
214 may also be communicatively coupled to a home subscriber server
(HSS) 224, which stores subscriber information, including
information about the WCD 202-1 and/or WCD 202-3. For cellular
voice communications, the eNodeB may connect to a MSC 220 by way of
an interworking function IWF 212 communicatively connected between
the MME 212 and the MSC 220. The MSC 220 may then provide
connectivity of a PSTN 226, as shown.
For communications under CDMA based protocols, subscribers may
engage in communications via the BTS 206 and the associated antenna
206-T from the WCD 202-2 over air interface 203-1 and/or from the
WCD 202-3 over air interface 203-2. Transmissions over the air
interface 203-1 from the antenna 206-T to the WCD 302-2 represent a
"forward link" from the CDMA/EVDO BTS 206 to the WCD 202-2, while
transmissions over air interface 203-1 from the WCD 202-2 to the
antenna 206-T represent a "reverse link" from the WCD 202-2.
Similarly, transmissions over the air interface 203-2 from the
antenna 206-T to the WCD 202-3 represent a forward link, while
transmissions over air interface 203-2 from the WCD 202-3 to the
206-T represent a reverse link.
The CDMA BTS 206 may be connected to a BSC 210, which provides a
connection to the MSC 220 for cellular voice communications. The
MSC 220 acts to control assignment of air traffic channels (e.g.,
over air interfaces 203-1 and 203-2), and provides access to
wireless circuit-switched services such as circuit-voice and
circuit-data (e.g., modem-based packet data) service. As
represented by its connection to the PSTN 226, the MSC 220 may also
be coupled with one or more other MSCs, other telephony circuit
switches in the operator's (or in a different operator's) network,
or other wireless communication systems, thereby supporting user
mobility across MSC regions, roaming between systems, and local and
long-distance landline telephone services.
For packet data communications, the IWF 212 connected between the
BSC 210 and the MME 214 can support interworking between EVDO based
packet protocols and those of the LTE Advanced based network. Thus,
the BSC 210 may communicate on the internet 222 by way of the MME
214, the S-GW 216, and the PDN GW 218.
FIG. 3 is a simplified block diagram of an example of alternate RAN
configuration in which a CDMA/EVDO RAN and an LTE RAN are merged
into a single "multi-modal" RAN of a network 300. As shown, the
multi-modal RAN includes antenna system 304-A/B, where the label
"A/B" signifies that the antenna system supports at least two
different air-interface technologies arbitrarily labeled "A" for an
LTE Advanced based air interface, and "B" for CDMA based air
interface. The multi-modal antenna system 304-A/B can be considered
antenna and transceiver elements of a multi-modal access node 304,
which in turn includes a CDMA/EVDO BTS 406 for CDMA/EVDO based
communications and an eNodeB 308 for LTE Advance based
communication, each respectively coupled with the multi-modal
antenna system 304-A/B.
The example illustrated in FIG. 4 also shows three WCDs 302-1,
302-2, and 302-3. Each WCD is depicted as having at least one
active air interface of particular type with the antenna system
304-A/B. Specifically, the WCD 302-1 has an air interface 303-1;
the WCD 302-2 has an air interface 303-2; and the WCD 302-3 has two
air interfaces 303-3-A and 303-3-B. For purposes of illustration,
and by way of example, the air interfaces 303-1 and 303-3-A may be
taken to be LTE air interfaces, and the air interfaces 303-2 and
303-3-B may be taken to be CDMA/EVDO air interfaces. As in FIG. 2,
the LTE Advanced air interfaces are depicted as white-filled
"lightning bolts," and the CDMA air interfaces are depicted as
blackened "lightning bolts." The two air interfaces 303-3-A and
303-3-B depicted for the WCD 302-3 may be taken as representing a
capability of the WCD 302-3 to operate according to either air
interface separately, and/or to operate according to both
concurrently.
For communications under LTE Advanced based protocols, subscribers
may engage in communications via antenna system 304-A/B from the
WCD 302-1 over air interface 303-1 and/or from the WCD 302-3 over
air interface 303-3-A. Uplinks and downlinks are defined as in FIG.
2.
The eNodeB 308 may be connected to a serving gateway S-GW 316,
which in turn may be connected to an internet 322 via a packet data
network gateway PDN-GW 318. The eNodeB 308 could also be connected
to the S-GW 316 by way of a mobility management entity MME 314,
which may also be configured to control communications between the
eNodeB 308 and one or more other eNodeBs in the network. The MME
314 may also be communicatively coupled to a HSS 324, which stores
subscriber information, including information about the WCD 302-1
and/or WCD 302-3. For cellular voice communications, the eNodeB may
connect to a MSC 320 by way of an interworking function IWF 312
communicatively connected between the MME 312 and the MSC 320. The
MSC 320 may then provide connectivity of a PSTN 326, as shown.
For communications under CDMA/EVDO based protocols, subscribers may
engage in communications via antenna system 304-A/B from the WCD
302-2 over air interface 303-2 and/or from the WCD 302-3 over air
interface 303-3-B. Forward and reverse links are defined as in FIG.
2, except now both CDMA/EVDO forward and reverse links and LTE
uplinks and downlinks may share a common antenna system 304-AB in
the multi-modal RAN.
The CDMA/EVDO BTS 306 may be connected to a BSC 310, which provides
a connection to the MSC 320 for cellular voice communications. The
MSC 320 acts to control assignment of air traffic channels (e.g.,
over air interfaces 303-2 and 303-3-B), and provides access to
wireless circuit-switched services such as circuit-voice and
circuit-data (e.g., modem-based packet data) service. As
represented by its connection to the PSTN 326, the MSC 320 may also
be coupled with one or more other MSCs, other telephony circuit
switches in the operator's (or in a different operator's) network,
or other wireless communication systems, thereby supporting user
mobility across MSC regions, roaming between systems, and local and
long-distance landline telephone services.
For packet data communications, the IWF 312 connected between the
BSC 310 and the MME 314 can support interworking between CDMA/EVDO
based packet protocols and those of the LTE Advanced based network.
Thus, the BSC 410 may communicate on the internet 322 by way of the
MME 314, the S-GW 316, and the PDN GW 318.
It should be understood that the depiction of just one of each
network element in each of FIGS. 2 and 3 is illustrative, and there
could be more of any of them, as well as other types of elements
not shown. The particular arrangements shown in FIGS. 2 and 3
should not be viewed as limiting with respect to the example
embodiments presented herein. Further, the network components that
make up a wireless communication system such as network 200 or 300
are typically implemented as a combination of one or more
integrated and/or distributed platforms, each comprising one or
more computer processors, one or more forms of computer-readable
storage (e.g., disks drives, random access memory, etc.), one or
more communication interfaces for interconnection between elements
and the network and operable to transmit and receive the
communications and messages described herein, and one or more
computer software programs (or other forms of computer logic
instructions) and related data (e.g., machine-language instructions
and program and user data) stored in the one or more forms of
computer-readable storage and executable by the one or more
computer processors to carry out the functions, steps, and
procedures of the various example embodiments described herein.
Similarly, a communication device such as example WCDs 202-1,
202-2, and 202-3, and WCDs 302-1, 302-2, and 302-3 typically
comprises a user-interface, I/O components, a communication
interface, a tone detector, a processing unit, and data storage,
all of which may be coupled together by a system bus or other
mechanism. As such, networks 200 and 300, WCDs 202-1, 202-2, and
202-3, and WCDs 302-1, 302-2, and 302-3, and air interfaces 203-1,
203-2, 207-1, and 207-2, and 303-1, 303-2, 303-3-A, and 303-3-B
collectively are representative of example means of implementing
and carrying out the various functions, steps, and procedures
described herein.
1. Example Access Technologies
a. Conventional CDMA Communications
In a conventional CDMA wireless network compliant with the well
known IS-2000 standard, each cell employs one or more carrier
frequencies, typically 1.25 MHz in bandwidth each, and each sector
is distinguished from adjacent sectors by a pseudo-random number
offset ("PN offset"). Further, each sector can concurrently
communicate on multiple different channels, distinguished by "Walsh
codes." In doing so, each channel is allocated a fraction of the
total power available in the sector. When a WCD operates in a given
sector, communications between the WCD and the BTS of the sector
are carried on a given frequency and are encoded by the sector's PN
offset and a given Walsh code. The power allocated to each channel
is determined so as to optimize the signal to noise characteristics
of all the channels, and may vary with time according to the number
of WCDs being serviced, and their relative positions with respect
to the BTS, among other factors.
Air interface communications are divided into forward link
communications, which are those passing from the base station to
the WCD, and reverse link communications, which are those passing
from the WCD to the base station. In an IS-2000 system, both the
forward link and reverse link communications in a given sector are
encoded by the sector's PN offset and a given Walsh code. On the
forward link, certain Walsh codes are reserved for use to define
control channels, including a pilot channel, a sync channel, and
one or more paging channels (depending on service demand, for
example), and the remainder can be assigned dynamically for use as
traffic channels, i.e., to carry user communications. Similarly, on
the reverse link, one or more Walsh codes may be reserved for use
to define access channels, and the remainder can be assigned
dynamically for use as traffic channels.
In order to facilitate efficient and reliable handoff of WCDs
between sectors, under IS-2000 a WCD can communicate on a given
carrier frequency with a number of "active" sectors concurrently,
which collectively make up the WCD's "active set." Depending on the
system, the number of active sectors can be up to six (currently).
The WCD receives largely the same signal from each of its active
sectors and, on a frame-by-frame basis, selects the best signal to
use. A WCD's active set is maintained in the WCD's memory, each
active sector being identified according to its PN offset. The WCD
continually monitors a pilot signal from each of its active sectors
as well as from other sectors, which may vary as the WCD moves
about within the wireless communication system, or as other factors
cause the WCD's RF conditions to change. More particularly, the WCD
monitors a signal-to-noise metric referred to as "signal to
interference plus noise ratio" ("SINR"), which includes the
degrading effects of interference as well as noise on RF
conditions. The WCD reports the received signal strengths to the
serving base station, which then directs the WCD to update its
active set in accordance with the reported strengths and one or
more threshold conditions. Note that a WCD's active set can include
a femtocell.
Typically, the power level of the pilot detected by a WCD is
specified as a gain level, x, according to the relation x dBm=10
log.sub.10(P/1 mW), where P is the power in mW (milliwatts).
However, other power units could be specified. Measured in dBm,
gain expresses a logarithmic ratio of power P to a fixed power
level of 1 mW. More generally, the relative gain, y, of one power
level P.sub.1 to another P.sub.2 is expressed as dB, and
corresponds to a logarithmic ratio of P.sub.1 to P.sub.2 given by y
dB=10 log.sub.10(P.sub.1/P.sub.2). For instance, if y=3, then
P.sub.1.apprxeq.2.times.P.sub.2; if y=-3, then
P.sub.1.apprxeq.0.5.times.P.sub.2. In practice, SINR is measured in
dB, where P.sub.1 corresponds to the received power of the pilot
and P.sub.2 corresponds to the received noise plus interference
power.
b. High Rate Packet-Data TDM Communications
Under IS-2000, the highest rate of packet-data communications
theoretically available on a fundamental traffic channel of the
forward link is 9.6 kbps, dependent in part on the power allocated
to the forward-link traffic channel and the resultant signal to
noise characteristics. In order to provide higher rate packet-data
service to support higher bandwidth applications, the industry
introduced a new "high rate packet data (HRPD) system," which is
defined by industry standard IS-856 (or EVDO).
IS-856 leverages the asymmetric characteristics of most IP traffic,
in which the forward link typically carries a higher load than the
reverse link. Under IS-856, each WCD maintains and manages an
active set as described above, but receives forward-link
transmission from only one active sector at a time. In turn, each
sector transmits to all its active WCDs on a common forward link
using time division multiplexing (TDM), in order to transmit to
only one WCD at a time, but at the full power of the sector. As a
result of the full-power allocation by the sector, a WCD operating
under IS-856 can, in theory, receive packet-data at a rate of at
least 38.4 kbps and up to 2.4 Mbps. The reverse link under IS-856
retains largely the traditional IS-2000 code division multiplexing
(CDM) format, albeit with the addition of a data rate control (DRC)
channel used by the WCD to indicate the supportable data rate and
best serving sector for the forward link. More specifically, the
WCD monitors SINR on the forward link from its serving sector (or
base station) to determine a data rate to request. The requested
data rate is encoded in a DRC request, and transmitted to the
serving base station on the DRC channel, which is a sub-channel of
a reverse-link Medium Access Control (MAC) channel.
TDM access on the IS-856 forward link is achieved by dividing the
forward link in the time domain into time slots of length 2048
chips each. At a chip rate of 1.228 Mega-chips per second, each
slot has a duration of 1.67 milliseconds (ms). Each time slot is
further divided into two 1024-chip half-slots, each half-slot
arranged to carry a 96-chip pilot "burst" (pilot channel) at its
center and a forward-link MAC channel in two 64-chip segments, one
on each side of the pilot burst. The remaining 1600 chips of each
time slot (800 per half-slot) are allocated for a forward traffic
channel or a forward control channel, so that any given time slot
will carry either traffic-channel data (if any exists) or
control-channel data. As in IS-2000, each sector in IS-856 is
defined by a PN offset, and the pilot channel carries an indication
of the sector's PN offset. Again, a sector could correspond to a
femtocell.
c. LTE Advanced Communications
Under LTE Advanced, the downlink comprises multiple frequency
carrier bands arranged to cover a total bandwidth of up to 20 MHz
(currently) in frequency space. Each frequency carrier band is
divided into 12 orthogonal subcarrier frequencies, each 15 kHz in
width, for a total of 180 kHz per frequency carrier band. The
number of frequency carrier bands corresponds to the integer
division of the total bandwidth by 180 kHz. For example, a total
bandwidth of 1.25 MHz supports six frequency carrier bands; a total
bandwidth of 20 MHz supports 100 frequency carrier bands. The
orthogonality of the subcarrier frequencies follows from each being
an integer multiple of the same minimum frequency; e.g., 15 kHz. It
will be appreciated that a different minimum frequency could be
used, as long as the orthogonality condition is met. Similarly, a
different number of subcarrier frequencies per frequency carrier
band could be used, which could then lead to a different number
frequency carrier bands for a given total bandwidth.
In the time domain, the downlink comprises time slots, each
typically of 0.5 msec duration. Every two time slots makes up one
"sub-frame" of 1.0 msec duration, and every 10 sub-frames makes up
a 10 msec frame. Each time slot is subdivided into an integer
number of symbol durations, such that the integer number multiplied
by the symbol duration equals 0.5 msec. According to current
standards, the integer number is either 6 or 7; the value used
depends on operating conditions, among other possible factors. For
the purposes of the present discussion the integer number of symbol
durations per time slot will be taken to be 7, with the
understanding that other values could be used.
Transmissions on the downlink are scheduled in time-frequency units
referred to as "resource blocks" or RBs. Each RB is made up of 7
contiguous symbol durations (i.e., one time slot) and 12 subcarrier
frequencies of a given frequency carrier band. Thus, an RB can be
viewed a grid of 7 symbol durations by 12 subcarrier frequencies.
Each element of the grid is referred to as "resource element," and
each resource element carries one OFDM symbol. Each OFDM symbol of
a resource element is a time domain symbol generated from Fourier
superposition frequency domain symbols.
A single RB is the smallest unit of allocation made for a given WCD
for downlink transmissions. Allocations are typically made by an
eNodeB serving the WCD, and more than one RB can be allocated for
the WCD. Multiple RB allocations for a given WCD can be made across
multiple frequency carrier bands, across multiple time slots, or
both, depending on factors including the amount of data to be
transmitted to the WCD, the type of data (e.g., best-effort,
real-time, etc.), and downlink resources needed for other WCDs.
In addition to carrying OFDM symbols specific to a given WCD,
particular resource elements of a given RB are allocated as
"reference signals," and may be used to carry pilot signals from
the eNodeB. Upon detection of a pilot signal in one or more
resource elements of an RB, a WCD may determine SINR of the eNodeB
(or more generally, the LTE Advanced base station) that made the
RB-based transmission. The WCD may then use the SINR (or other SNR
measure) of different eNodeBs that it detects to determine if and
when to hand off from one to another, for example.
2. Spectral Efficiency as a Basis for Selecting and Air Interface
Protocol
When a WCD sends a request to an LTE RAN (or LTE eNodeB) for data
service, it can include in the request an indicator of quality of
at least one channel as observed by the WCD based on
signal-to-noise ratio or SINR, for example. The indicator, referred
to as a "channel quality indicator" (CQI), may be used by the LTE
RAN to determine a coding modulation scheme and data rate to use
for the requested data service with the WCD. If the LTE RAN is
co-located with an EVDO RAN--for example, if the LTE eNodeB is
co-located with an EVDO BTS--or if the WCD is sufficiently within
range of both the LTE RAN and the EVDO RAN, the LTE RAN will
conventionally grant the data service request without necessarily
determining if the EVDO RAN might be a suitable choice for
providing the service. This conventional operation accounts for the
typically higher data rates supported by LTE compared with
EVDO.
However, it can happen that the spectral efficiency (bits per
second per Hz) for providing the service is relatively low on the
LTE interface compared with an average spectral efficiency on the
LTE interface, and that the spectral efficiency for providing the
service is relatively of the EVDO interface that EVDO service is at
the same time relatively high. For example, the LTE eNodeB may be
highly loaded (in terms of a number of WCDs being concurrently
served) and/or the WCD might measure a low SNR, resulting in a
relatively lower spectral efficiency for LTE service, even at a
data rate commensurate with that projected for EVDO service. At the
same time, if the EVDO base station is lightly loaded (in terms of
a number of WCDs being concurrently served) and/or the WCD measures
a high SINR, the data rate available for providing the service on
the EVDO interface at the time of the request might correspond to a
high spectral efficiency for EVDO service. Under circumstances such
as these, an aggregate spectral efficiency of the LTE RAN and the
EVDO RAN might be increased (or at least more advantageously
managed) by granting the WCD's service request using the EVDO air
interface.
In accordance with example embodiments, a determination as to which
of an LTE air interface and an EVDO air interface to select for
providing a requested data service to a WCD, when both air
interfaces are available, may be made by evaluating the relative
spectral efficiencies of the two air interfaces for providing the
requested service. More particularly, when a WCD sends a request
for data service to an LTE eNodeB, the LTE RAN or other network
element can determine a requested spectral efficiency associated
with the request. If the requested spectral efficiency exceeds
reference level, then the requested service will be provided by the
LTE RAN (i.e., the LTE eNodeB that received the request). If the
requested spectral efficiency does not exceed the reference level,
the LTE RAN or other network element) can determine a projected
spectral efficiency for providing the service by the EVDO RAN, and
then, in a manner described below, can compare the requested
spectral efficiency on the LTE air interface with the projected
spectral efficiency on the EVDO interface to determine which of the
LTE RAN or the EVDO RAN to select for providing the service.
In accordance with example embodiments, the CQI sent by a WCD in
its request to an LTE eNodeB can be used to determine a requested
spectral efficiency .eta..sub.LTE associated with providing the
requested service. Specifically, the WCD includes the CQI encoded
as a 4-bit integer, referred to a "CQI index" that can be used in a
CQI look-up table to determine an LTE spectral efficiency (as well
as the modulation scheme and data rate).
Upon receiving a data service request from a WCD on its LTE air
interface, an LTE eNodeB can send the included CQI index to a
network device communicatively coupled with both the LTE eNodeB and
the EVDO BTS (or base station). By way of example, the network
device could be part of the LTE eNodeB, another element of the LTE
RAN, or a network node of the wireless communication system. The
network device could use the CQI index to determine a requested
spectral efficiency associated with the WCD's service request. For
example, the network device could look up the requested spectral
efficiency .eta..sub.LTE in a CQI table. Alternatively, the eNodeB
could determine the requested spectral efficiency and send it to
the network device.
FIG. 4 is an example CQI table 400 that could be stored in
non-transient media in or associated with the network device. As
shown, the CQI table 400 includes four columns: CQI Index,
Modulation, Code Rate, and Spectral Efficiency (bits/Hz). The CQI
index is a four bit integer in the inclusive range of [1, 15]. This
is included by a WCD in its request for data service to an LTE
eNodeB. For purposes of the present discussion, it may be seen that
each CQI index value is associated with a spectral efficiency in
the fourth column. Note that as defined in the CQI table 400,
spectral efficiency is corresponds to bits per Hz, and can be
greater than one. In accordance with example embodiments, the
network device can determine the requested spectral efficiency for
a WCD data service request by looking up a value in the fourth
column of the CQI table 400 (or the like) based on the CQI index
received from the WCD by way of the LTE eNodeB.
As described, .eta..sub.LTE is based on a SNR or SINR measurement
by the WCD at the time it makes its request for service. Thus, it
may be considered as reflecting current conditions in the cell or
sector of the LTE eNodeB. In accordance with example embodiments,
the network device can also determine an average spectral
efficiency <.eta..sub.LTE> of data communication services
provided by the LTE eNodeB over some specified time window. For
example, the time window could stretch backward for 10-20 minutes
from the time of the WCD's request. Other time durations could be
used as well. The network device could obtain a historical record
of CQI indexes received in data service requests from WCDs during
the time window, and convert the CQI indexes to corresponding
historical spectral efficiencies using the CQI table 400, for
example. An average spectral efficiency <.eta..sub.LTE> could
then be determined as time average of the historical spectral
efficiencies. The time average could be a simple average of the
historical spectral efficiencies, or a weighted average in which
each historical spectral efficiency is weighted by a duration of
how long the spectral efficiency was applied in the associated data
communication service. Other particular formulas for deriving
average spectral efficiency could be devised as well.
In further accordance with example embodiments, the network device
could compute a first ratio of the requested spectral efficiency to
the average spectral efficiency,
.eta..eta. ##EQU00001## and compare the ratio to a threshold value.
If the ratio is greater than or equal to a threshold value,
R.sub.1.gtoreq.Threshold, then the network device could select the
LTE eNodeB to provide the requested service on the LTE air
interface. If the ratio is less than the threshold value,
R.sub.1<Threshold, then the network device could determine a
projected spectral efficiency for providing the requested service
on the EVDO air interface of the EVDO RAN (e.g., EVDO BTS), and
could further determine an average spectral efficiency of service
provided on the EVDO air interface. The network device could then
compute and compare a ratio of the requested-to-projected spectral
efficiencies to a ratio of the LTE average spectral efficiency to
the EVDO average spectral efficiency in order to determine which
air interface to select for granting the WCD's requested service,
as described below.
In accordance with example embodiments, the network device could
determine the projected spectral efficiency .eta..sub.DO by first
determining a projected data rate for providing the data service on
the EVDO interface, and dividing the result by the channel
bandwidth (e.g., 1.25 MHz for EVDO). The projected data rate could
be determined by querying the WCD for a DRC value that the WCD
would use if it were to request the data service from the EVDO RAN
instead. The request could be made via the LTE eNodeB, for example.
Upon receiving the DRC, the network device could then determine a
corresponding data rate by decoding the DRC value. For example, the
network device could look up the data rate in a DRC table using the
DRC value from the WCD.
FIG. 5 is an example DRC table 500 that could be stored in
non-transient media in or associated with the network device, and
used for looking up a projected data rate based on a DRC value
reported by a WCD. The same or similar table may be stored in the
WCD and consulted when the WCD makes a data service request. As
shown, the DRC table 500 has four columns: column 502 lists SINR
threshold values in dB in increasing order; column 504 lists the
corresponding DRC codes; column 506 lists the corresponding
numerical data rates; and column 508 lists number of timeslots
required for transmitting a packet at the corresponding data rate
and DRC code. The SINR thresholds in column 502 are applied by the
WCD as upper limits, such that the WCD determines the smallest SINR
threshold value that is greater than (but not equal to) a given
SINR measured by the WCD, and selects the preconfigured DRC code
corresponding with the determined largest SINR threshold value. For
example, for a measured SINR of -3.2 dB, the WCD would determine
the smallest SINR threshold value larger than the measured one to
be -2.8 dB, corresponding to a DRC code of 3 and a forward-link
data rate of 153.6 kbps.
Were the WCD making a data service request, it would then send the
DRC code in the request to the EVDO base station. In the currently
described example embodiment, the WCD will just report the DRC code
to the LTE eNodeB, which will then send the code to the network
device. The network device can then use the reported DRC code to
look up the corresponding projected data rate in the third column
506 of the DRC table 500. Dividing the projected data rate by the
channel bandwidth would then give the project spectral efficiency
f.sub.DO.
In further accordance with example embodiments, the network device
could determine an average EVDO spectral efficiency
<.eta..sub.DO> in a manner similar that for determining
<f.sub.LTE>. Specificlly, the network device query the EVDO
BTS (or other element of the EVDO RAN) to obtain DRC values used
for servicing data requests over a time window stretching back from
the current time (e.g., the time that the WCD's request to the LTE
eNodeB was received). The time window could be the same as that
used for computing the average LTE spectral efficiency, for
example. The historical DRC values could be used to determine
historical data rates and corresponding historical EVDO spectral
efficiencies. An average EVDO spectral efficiency <f.sub.DO>
could then be determined in a manner similar to that described
above data service for the average LTE spectral efficiency.
The network device could then compute a current spectral efficiency
ratio as a ratio of the projected EVDO spectral efficiency to the
requested LTE spectral efficiency,
.eta..eta. ##EQU00002## Similarly, the network device could compute
a ratio of the average EVDO spectral efficiency to the average LTE
spectral efficiency,
.eta..eta. ##EQU00003## If the current spectral efficiency ratio is
less than or equal the average spectral efficiency ratio,
R.sub.cur.ltoreq.R.sub.avg, then the network device could select
the LTE eNodeB to provide the requested service on the LTE air
interface. If instead, the current spectral efficiency ratio is
greater than the average spectral efficiency ratio,
R.sub.cur>R.sub.avg, then the network device could select the
EVDO base station (BTS) to provide the requested service on the
EVDO air interface.
Selection of which air interface to use based on the spectral
efficiencies, as just described for example, can help balance the
generally higher data rates supported under LTE against a
distribution of provided data services between LTE and EVDO in a
way that enhances an aggregate or overall spectral efficiency of
providing data services over both air interface technologies. This
can be seen by considering the algebraic inequalities used in
comparing the spectral efficiency ratios above. Specifically, the
inequality R.sub.cur<R.sub.avg can be algebraically rearranged
as
.eta..eta..gtoreq..eta..eta. ##EQU00004## Defining the ratio
.eta..eta. ##EQU00005## and taking
.eta..eta. ##EQU00006## as defined above, the inequality
.eta..eta..gtoreq..eta..eta. ##EQU00007## becomes
R.sub.1.gtoreq.R.sub.2. The selection of the air interface based on
spectral efficiencies can then be summarized as:
If
.eta..eta. ##EQU00008## .gtoreq.Threshold, then select the LTE air
interface. (1)
If Threshold>
.eta..eta..gtoreq..eta..eta. ##EQU00009## then select the LTE air
interface. (2)
If Threshold>
.eta..eta..times..times..eta..eta.>.eta..eta. ##EQU00010## men
select the EVDO air interface. (3)
Condition (1) corresponds to a requested (current) LTE spectral
efficiency that is sufficiently high compared with the average LTE
spectral efficiency as to make selection of the LTE air interface a
good choice. For example, if threshold is greater than one
(Threshold>1), the condition (1) indicates that
.eta..sub.LTE.gtoreq.<.eta..sub.LTE>, so providing the
requested data service on the LTE air interface will tend to
increase the average LTE spectral efficiency of the LTE eNodeB. The
threshold need not be greater than one, as discussed in the
numerical example below.
Condition (2) indicates that while the requested (current) LTE
spectral efficiency is not higher than a threshold level compared
with the average LTE spectral efficiency, it is nevertheless
proportionally higher than the projected EVDO spectral efficiency.
The proportionality is contained in the ratios R.sub.1 and R.sub.2.
Thus, providing the requested data service on the LTE air interface
is still preferable to providing the requested service on the EVDO
air interface.
Condition (3) indicates that the requested (current) LTE spectral
efficiency is not only below the threshold level compared with the
average LTE spectral efficiency, but it is also proportionally
lower than the projected EVDO spectral efficiency. Again, the
proportionality is contained in the ratios R.sub.1 and R.sub.2.
Thus, providing the requested data service on the EVDO air
interface may tend to increase an aggregate or overall spectral
efficiency of both the LTE and EVDO air interfaces.
The following numerical example further illustrates how selection
of an air interface based on spectral efficiency may operate in
example practical circumstances. For the numerical example, it is
assumed that an "expected average LTE spectral efficiency,"
E[.sub.LTE)], may be determined for the LTE air interface. For
example, E[.sub.LTE] could be an average over multiple LTE air
interfaces of a wireless communication system, and/or could
correspond to a longer-term average than the average LTE spectral
efficiency <.sub.LTE>, such as an average over many hours,
days, or even longer. It could also be based on time of day, such
as a busy-time average and/or quiet-time average. In contrast,
<.sub.LTE> can be taken to apply to a particular LTE air
interface at which a service request is received, and/or might
correspond to a rolling time average over a shorter time window,
such as minutes or tens of minutes, for example. In a similar way,
it is assumed that an analogous "expected average EVDO spectral
efficiency," E[.sub.DO], may be determined for the EVDO air
interface.
In accordance with example embodiments, the threshold value can be
set with reference to E[.sub.LTE] and E.eta..sub.DO] by considering
a sort of "target" case in which
<.sub.LTE>.apprxeq.E[.sub.LTE] and
<.sub.DO>.apprxeq.E[.sub.DO], and stipulating that the
requested spectral efficiency .sub.LTE be at least as high as
E[.sub.DO] in order to sufficiently warrant selection of the LTE
air interface. A sufficient condition for selecting the LTE air
interface can then be expressed as .sub.LTE.gtoreq.E[.sub.DO].
Dividing both sides of this expression by E[.sub.LTE] gives
.eta..function..eta..gtoreq..function..eta..function..eta.
##EQU00011## Finally, since E[.sub.LTE].apprxeq.<.sub.LTE>,
this can be written as
.gtorsim..function..eta..function..eta. ##EQU00012## winch
essentially the same as condition (1), expect for the approximate
instead of strict equality. This reasoning therefore suggests using
threshold value of Threshold=
.function..eta..function..eta. ##EQU00013##
For purposes of the present illustration, and by way of example,
let E[.sub.LTE)]=2.29 and let E[.sub.DO]=0.66. These values may be
representative of typical system performance, although it will be
appreciated that other values could be used. They also fall
approximately midrange in the CQI table 400 and the DRC table 500,
respectively. Based on these example values, it follows that
Threshold=0.288 in conditions (1)-(3) above. In particular,
condition (1) corresponds to selection of the LTE air interface if
R.sub.1.gtoreq.0.288, or <.sub.LTE.gtoreq.0.66 (by design in
this example). Referring again to the CQI table 400 in FIG. 4, this
would be the case for CQI indexes.gtoreq.5. For R.sub.1<0.228,
conditions on the EVDO air interface need to be evaluated to
determine which of conditions (2) or (3) then applies.
Specifically, if
>.gtoreq..eta..eta. ##EQU00014## (condition (2)), then the LTE
air interface is still selected. If instead
<.eta..eta. ##EQU00015## condition (3)), then the EVDO air
interface is selected. As noted above, one rationale for condition
(3) is that in this case .sub.LTE is a smaller fraction of
<.sub.LTE> than .sub.DO is of <.sub.DO>, suggesting
that service on the EVDO air interface may more favorably
contribute to overall spectral efficiency than service on the LTE
air interface. A refinement of this rationale can be to set a limit
to how small
.eta..eta. ##EQU00016## can be, even when R.sub.1<R.sub.2, in
order to warrant selection of the EVDO air interface. This can be
accomplished by introducing an additional threshold, T.sub.DO, for
setting a lower limit to R.sub.2 and modifying condition (3) as
follows.
If Threshold>
.eta..eta..times..times..eta..eta.>.eta..eta..times..times..eta..eta..-
gtoreq. ##EQU00017## then select the EVDO air interface. (3a)
If Threshold>
.eta..eta..times..times..eta..eta.>.eta..eta..times..times..eta..eta.&-
lt; ##EQU00018## then select the LTE air interface. (3b)
Application of conditions (3a) and (3b) can be illustrated with a
numerical example. Specifically, let T.sub.DO=0.66. Again
taking
<.eta.>.apprxeq..function..eta..times..times..eta..eta..gtoreq.
##EQU00019## corresponds to
.eta..sub.DO.gtoreq.0.66.times.0.66=0.436. Referring again to the
DRC table 500 in FIG. 5, condition (3a) can be seen to correspond
to DRC code values.gtoreq.6, while condition (3b) corresponds to
DRC code values.ltoreq.5.
It will be appreciated that the numerical examples above could be
adapted to other values of Threshold and (if applicable)
T.sub.DO.
a. Example Method Implementation
Selection of an air interface based on spectral efficiency can be
implemented as logical instructions that can stored in
non-transient media of a network device, and executed by one or
processors of the network device. FIG. 6 is a flowchart depicting
an example program logic of an example implementation of a method
of selection of an air interface protocol based on spectral
efficiency, in accordance with example embodiments. The flowchart
begins at step 602, which marks the start of the procedure.
At step 602 a service request from a WCD is received at an LTE air
interface of an LTE RAN. For example, the request could be received
at an LTE air interface of an LTE eNodeB.
At step 606, a requested LTE spectral efficiency .sub.LTE for
providing the service on the LTE air interface is determined.
At step 608, an average LTE spectral efficiency <.sub.LTE>
for WCDs being served by the LTE RAN is determined.
At step 610, a LTE spectral efficiency ratio
.eta..eta. ##EQU00020## is determined, and at step 612, the
determined R.sub.1 is compared with a threshold.
If the determination at step 612 is that R.sub.1.gtoreq.threshold
("Yes" branch from step 612), then at step 614 requested service is
granted on the LTE air interface of the LTE RAN. The procedure then
ends at step 616.
If the determination at step 612 is that R.sub.1<threshold ("No"
branch from step 612), then the procedure advances to step 613,
where a projected EVDO spectral efficiency .eta..sub.DO for
providing the service on an EVDO air interface is determined. The
EVDO RAN could be co-located with the LTE RAN, or could be
neighboring such that it is capable of providing the WCD's
requested service.
At step 615, an average EVDO spectral efficiency <.sub.DO>
for WCDs being served by the EVDO RAN is determined.
At step 617, an EVDO spectral efficiency ratio
.eta..eta. ##EQU00021## is determined, and at step 619, the
determined R.sub.2 is compared with R.sub.1.
If the determination at step 619 is that R.sub.1.gtoreq.R.sub.2
("Yes" branch from step 619), then the procedure advances to step
614, where, again, the requested service is granted on the LTE air
interface of the LTE RAN. The procedure then ends at step 616.
If the determination at step 619 is that R.sub.1<R.sub.2 ("No"
branch from step 619), then the procedure advances to step 621,
where the requested service is granted on the EVDO air interface of
the EVDO RAN. The procedure then ends at step 623.
b. Example network device FIG. 7 is a simplified block diagram
depicting functional components of an example network device 702 in
which an example embodiment of selection of an air interface
protocol based on spectral efficiency could be carried implemented.
As shown in FIG. 7, the example network device 702 includes a
transceiver 704, network interface 706, a processing unit 714, and
data storage 708, all of which may be coupled together by a system
bus 716 or other mechanism. In addition, the network device 702 may
also include external storage, such as magnetic or optical disk
storage, although this is not shown in FIG. 7. By way of example,
the network device could be an IWF (such as IWF 212 in FIG. 2 or
IWF 312 in FIG. 3), an MME (such as MME 214 in FIG. 2 or MME 314 in
FIG. 3), or an eNodeB (such as eNodeB 208 in FIG. 2 or eNodeB 308
in FIG. 3).
These components may be arranged to support wireless communications
in a wireless communication network that is compliant with a
variety of wireless air-interface protocols, such as networks 200
and/or 300 illustrated in FIGS. 2 and 3, respectively. In
particular, these components can support selection of an air
interface protocol based on spectral efficiency, in accordance with
example embodiments.
Network interface 706 enables communication on a network, such
networks 200 or 300. As such, network interface 706 may take the
form of an Ethernet network interface card or other physical
interface to a broadband connection to the internet or some other
data network. Further, a network device implemented as part of an
eNodeB, for example, may also include a transceiver 704, which may
include one or more antennas, enables air interface communication
with one or more WCDs, supporting both downlink and uplink
transmissions.
Processing unit 714 comprises one or more general-purpose
processors (e.g., INTEL microprocessors) and/or one or more
special-purpose processors (e.g., dedicated digital signal
processor, application specific integrated circuit, etc.). In turn,
the data storage 708 comprises one or more volatile and/or
non-volatile storage components, such as magnetic or optical memory
or disk storage. Data storage 708 can be integrated in whole or in
part with processing unit 714, as cache memory or registers for
instance. As further shown, data storage 708 is equipped to hold
program logic 710 and program data 712.
Program data 712 may comprise data such as a CQI table and/or a DRC
table, as well as a threshold. Program logic 710 may comprise
machine language instructions that define routines executable by
processing unit 714 to carry out various functions described
herein. In particular the program logic, communication interface,
and transceiver may operate cooperatively to carry out logical
operation, such as that described by way of example in FIG. 6, as
well other functions discussed above.
It will be appreciated that there can be numerous specific
implementations of a network device, such as network device 702, in
which selection of an air interface protocol based on spectral
efficiency could be implemented. Further, one of skill in the art
would understand how to devise and build such an implementation. As
such, network device 702 is representative of means for carrying
out selection of an air interface protocol based on spectral
efficiency, in accordance with the methods and steps described
herein by way of example.
4. Conclusion
An example embodiment has been described above. Those skilled in
the art will understand, however, that changes and modifications
may be made to this embodiment without departing from the true
scope and spirit, which is defined by the claims.
* * * * *